The invention relates to a method for ultrasound welding of two bag foils to a spout.
Bags as storage and transport containers for beverages and other liquid and pourable materials are known in the art and have recently found increasing acceptance because they are low-weight and require less space than cans, bottles or other rigid containers when empty. However, it is a desirable to provide these flexible bags with a closure which can be re-closed. For this purpose, a closure (spout) having a foot with, for example, a substantially elliptical, round, diamond-shaped or lens-shaped cross-section is welded between the edges of the bag foils of the bag (pouch). Such spout is typically welded in three consecutive steps requiring several, progressively narrower tools. A problem arises in the region where the two edges of the bag exhibit a sudden increase in height at the location where the closure is received. Welding causes plasticization of the edges and of the closure, requiring application of additional pressure with narrower tools. However, this cannot be precisely carried out, causing capillaries and other leakages these locations. Problems are caused not only by the tolerances of the individual components, but also by the tolerances of the welding machine and the welding tools and the welding motion itself. Because the closure must not only be welded to empty bags, but also to already filled bags, i.e., inline in the filling machine, there is a great need to attain a leak-tight weld.
For example, EP 1 245 500 A1 discloses a bag in which such closure has been welded. The very flat run-out or wing-like ends of the closure can be clearly seen, which help to keep the increase in height of the abutting edges of the bag as small as possible.
The publication “DIE—DIE ERNÄHRUNGSINDUSTRIE 3/2007; Article: Alternatives to Cans, Glass Containers and Bottles” mentions a frequent use of prefabricated bags. These prefabricated bags consist of two plastic or composite foils which are partially welded together, but which are still open on one side to allow filling. After filling, the spout is inserted and the open side of the bag is closed in several welding operations.
It is the object of the invention to provide a method for producing a bag with a spout, by which the bag can be produced by a simpler process.